1. Field of the Invention
The present invention relates to a lithographic plate fastening apparatus fastening a lithographic plate to a plate cylinder of a printing press in particular an offset press.
2. Description of the Related Art
In general, a presensitized plate or PS plate made of aluminium, paper plate and resin plate are known as a lithographic plate fastened to a plate cylinder of the offset press.
On one hand, the PS plate and resin plate, which are thick, can print on a large number of printing sheets and on the other hand, they are more expensive than the paper plate and the PS and resin plates which have been clamped by a vise must be fastened to the plate cylinder, so that attachment and detachment works of the PS and resin plates have been troublesome.
Therefore, a paper plate or thinner PS plate has been recently used when the number or printing sheets is small. However, these recent thinner plates are not firmer than conventional PS plates and resin plates, so that the recent thinner plates cannot be fastened directly to the plate cylinder. If they are directly fastened to the plate clyinder, a positioning etc. after a fastening of them to the plate cylinder may produce a wrinkle on them.
Therefore, when the thinner lithographic plate e.g. paper plate has been used in the prior art, a plate-fastening plate 53 fastening the thinner lithographic plate 52 e.g. paper plate to the top surface of a bite-side vise 51 of a plate cylinder 50 is provided as shown in FIGS. 27 and 28, a usual thick plate e.g. the PS plate previously fastened to the plate cylinder 50 constitutes a base plate 54 (a waste-after-use plate may be used as this base plate), and the lithographic plate 52 thinner than the base plate has been hooked on the plate-fastening plate 53 and fastened to the cylindrical surface of the base plate as a support.
When the thinner lithographic plate 52 is positioned relative to the plate cylinder 50, moving the base plate 54 with a thickness equal to that of the usual lithographic plate has moved the thinner lithographic plate 52 and base plate in unit.
The prior-art plate-fastening plate 53 is so arranged that when the thinner lithographic plate 52 e.g. paper plate is fastened to the plate cylinder 50, holes 52' in the lithographic plate 52 are hooked on a large number of hooks 53' provided on the plate-fastening plate 53. Therefore, the hooking is difficult when the breadth of that lithographic plate is great and the lithographic plate is often detached from the hooks 53' on which the lithographic plate has been once hooked, once the lithographic plate waves during a hooking work, so that fastening of the lithographic plate has been time-consuming.
In addition, since the bite-side vise 51 bites and fastens the hooks 53', a gap between a vise bed 5 and a clamping plate 12 must be adjusted by means of a spherical bolt when the usual PS plate is used instead of the paper plate and thinner PS plate. This adjustment is very troublesome.
Consequently, in a small-lot-of printing with the prior-art thinner lithographic plate, the time of exchanging the lithographic plate is longer than an actual printing time, so that a work efficiency has been much reduced.